1. Field of the Invention
The present invention relates to an apparatus and method for supporting an idle mode handover. More particularly, the present invention relates to an apparatus and method for supporting an idle mode handover in a heterogeneous wireless communication system.
2. Description of the Related Art
A next generation wireless communication system is evolving into a system for providing Mobile Stations (MSs) with various high-speed, high-capacity services. Representative examples of the next generation wireless communication system include a Worldwide Interoperability for Microwave Access (WiMAX) wireless communication system, a Long Term Evolution (LTE) wireless communication system, and the like. Among them, the WiMAX wireless communication system is based on Institute of Electrical and Electronics Engineers (IEEE) 802.16 wireless communication systems.
As is generally known in the art, an MS can access two different wireless communication systems by being provided with two radio interface units. Here, the MS may be a dual radio MS or a single radio MS according to whether or not the two radio interface units can simultaneously transmit data. That is, when the two radio interface units can simultaneously transmit data at a specific point of time, the MS is defined as a dual radio MS. Contrarily, when only one of the two radio interface units can transmit data at a specific point of time, the MS is defined as a single radio MS. However, in the case of both the dual radio MS and the single radio MS, the two radio interface units can simultaneously receive data.
If a single radio MS that has accessed a non-WiMAX wireless communication system detects a signal from a WiMAX wireless communication system, then the single radio MS scans a WiMAX Signal Forwarding Function (SFF) unit in order to perform a handover to the WiMAX wireless communication system. Here, the non-WiMAX wireless communication system refers to any wireless communication system other than the WiMAX wireless communication system. When the single radio MS discovers the WiMAX SFF unit, it performs a preregistration operation with the WiMAX wireless communication system through the WiMAX SFF unit. Upon performing this preregistration operation, the single radio MS may be immediately handed over to the WiMAX wireless communication system, or may transition to an idle mode, and then transition later to an active mode and be handed over to the WiMAX wireless communication system. Here, the former (that is, the case where the single radio MS is handed over immediately after the preregistration operation) is referred to as an active mode handover, and the latter (that is, the case where the single radio MS is handed over later on after the preregistration operation) is referred to as an idle mode handover.
According to an idle mode handover proposed in the current WiMAX wireless communication system, when a single radio MS in an idle mode moves from a preregistered Access Service Network GateWay (ASN_GW), and performs a handover to a Base Station (BS) connected to another ASN_GW, that is, a target ASN_GW, the target ASN_GW cannot know the address of a Home Agent (HA). Here, the preregistered ASN_GW refers to an ASN_GW with which the single radio MS has performed a preregistration operation.
Since the target ASN_GW cannot know the address of an HA, as mentioned above, the target ASN_GW cannot transmit a Mobile Internet Protocol (MIP) Registration ReQuest (RRQ) message (MIP RRQ message) to the HA.
In addition, in order to change a Foreign Agent (FA) of the single radio MS from the preregistered ASN_GW to the target ASN_GW, the target ASN_GW must perform an authentication operation with a Proxy MIP (PMIP) client. However, no procedure related to the PMIP authentication operation has been proposed in the current WiMAX wireless communication system.
In this way, since the target ASN_GW can neither transmit an MIP RRQ message to the HA nor perform an authentication operation with the PMIP client, it is not presently possible for the single radio MS, which has accessed the non-WiMAX wireless communication system, to achieve an idle mode handover to the WiMAX wireless communication system.